The invention relates to a synthetic bag with zig zag plies along the longitudinal sides, comprising a central and two outer zig zag ply longitudinal edges which define a first and a second zig zag plied part, the bag also having a filling valve on at least one of the final transverse sealed joints of the tubular foil constituting the bag.
Such a bag of synthetic material with zig zag plies and filling valve is known per se. This known synthetic bag has the drawback that this type of bag can only be used with difficulty which both filling machines with a vertical filling mouth and machines with a horizontal filling mouth. It is however desired in practice to utilize both types of filling machines. Therefore, after filling by means of e.g. a filling machine with a vertical filling mouth the entire valve should easily assume its original position, i.e. a position beside the final transverse sealed joint. This takes a certain retractive force, or a force exerted on the return valve.